FR2891688A1 - Fluid-heating device, has ring shape thermally-fusible part that partially fuses when area of electric heating units exceeds critical temperature threshold and moves switch from power supply configuration to power cut-off configuration - Google Patents

Abstract

Device has a switch (6) selectively moved between a configuration, in which electric heating units (4) are powered and a configuration, in which electric power supplied to the units is cut off. A ring shape thermally-fusible part (7) partially fuses when an area (8) of the units exceeds a critical temperature threshold and moves the switch (6) from the power supply configuration to the power cut-off configuration. The part is made up of an electrically non-conducting plastic material. The switch has a connection terminal formed on an outer surface (12) of a complementary element (3).

Description

FLUID HEATING DEVICE WITH THERMAL FUSE

  The present invention relates generally to the field of devices for electric heating of fluid.

  More particularly, the invention relates to a fluid heating device comprising a fluid circulation pipe, electric heating means arranged to heat the fluid passing through the fluid pipe, and a switch electrically connected to the electric heating means, this switch being selectively movable between a power configuration to allow the power supply of said electric heating means and a cut-off configuration to prohibit the power supply of said electric heating means.

  It may happen that such a heating device exceeds a critical temperature. Such a phenomenon occurs frequently in case of vacuum heating of the device, that is to say when the fluid line no longer carries enough fluid or more fluid at all.

  This phenomenon occurs for example in the event of failure of a thermostat for measuring a temperature of the device.

  In order to avoid the risk of overheating of the device, which may lead to a deterioration of the apparatus in which the device of the heater manufacturers is mounted, systems have been developed for disconnecting the electric heating means in the event of overheating.

  Document FR 2 778 729 discloses a device of the previously defined type comprising two thermostats connected in series at the electrical ends of the heating means. The probability of overheating of such an assembly is substantially equal to the product of the probabilities of malfunction of each of the two thermostats taken individually.

  It is also known from EP 0 485 211, a device of the previously defined type comprising a fuse mounted in series in the heating means in such a way that in case of overheating, the fuse melts and causes the power supply to stop. electric heating means. With such a system the power failure is not always frank for the same critical temperature.

  In this context, the present invention aims to propose a solution to cut the power supply of the electric heating means in case of overheating beyond a critical threshold of the fluid heating device.

  To this end, the device of the invention, moreover in accordance with the generic definition given in the preamble above, is essentially characterized in that a thermally fusible piece is disposed close to said electric heating means to be heated by these in operation, said fuse piece being adapted to melt at least partially when at least one zone of said electric heating means exceeds a critical temperature threshold and then to cause the switch to switch from its power configuration to its cutoff configuration.

  2891688 3 The combination of a movable switch between two configurations and a fuse whose function is to trigger, in case of overheating, the passage of the switch in cut-off configuration allows: - on the one hand to have a electric cutoff frank because of the design dedicated to this function of the switch; - On the other hand to benefit from reliable critical temperature threshold crossing detection due to the design dedicated to this function of the fuse piece.

  Thanks to the invention, the critical temperature threshold crossing detection and effective power cutoff detection functions are dissociated from each other thus allowing a dedicated design of an element to a function.

  For example, it is possible for the switch to have an elastic portion which naturally forces it to switch to a cut-off configuration, the thermally fusible part exerting a holding force of the switch in its power configuration as long as said zone of said electric heating means has not exceeded said critical temperature threshold.

  In this embodiment, as soon as the fuse piece is melted at least partially, the holding force is then no longer exerted on the switch which then passes by itself in cut-off configuration. The supply interruption here is irreversible until we have manually replaced the switch in its power position and as long as the fuse has not been replaced by a new part.

  It can also be made that the device comprises a main body and a complementary element covering a portion of the main body to define said pipe between the main body and an inner face of the complementary element, said switch comprising an electrically connected connection terminal the electric heating means and formed on an outer face of the complementary element which is opposite to said inner face.

  The fact of directly forming a terminal of the switch on the complementary element is advantageous because this: allows to simplify the connection of the switch with the electric heating means; eliminates the need for a connection cable between the terminal of the switch and the heating means; facilitates assembly operations of the device by reducing the number of parts needed for its manufacture.

  The connection terminal is preferably formed at one end of said electric heating means, thus this terminal is both an element of the electric heating means and a switch element, which is economically advantageous.

  It is also possible to make said switch comprise a metal contactor whose end is fixed on said main body, this contactor: selectively adopting a supply position where it is in contact with said connection terminal, the switch being then in power configuration and; selectively adopting a cut-off position in which it is separated from the connection terminal, the switch then being in cut-off configuration, said elastic portion of the switch being constituted by a locally elastic portion of the contactor which naturally forces the latter to switch to the break position.

  In this preferred embodiment of the invention, the switch is obtained simply by creating a metal contactor by folding / stamping a metal part (such as copper or stainless steel) and fixing it on the main body by one of its ends. During said folding / stamping, it is then easy to form: a first length portion of the rigid contactor whose function is to establish the electrical contact against a connection terminal; a second length portion of the rigid contactor having the function of being assembled on the main body, this assembly being able to be carried out for example by insertion of this second rigid contactor part into a complementary groove formed in the complementary body; a flexible and resilient portion disposed between the first and second rigid portions allowing these rigid portions to be movable between them elastically.

  This flexible portion allows the switch to be naturally monostable in its cut-off configuration.

  It can also be ensured that the electric heating means comprise at least one heating resistor screen printed on the outer face of the complementary element. By virtue of this embodiment, the heat produced by the resistor is directly transmitted to the water of the pipe through the wall formed by the complementary element, which minimizes heat losses and reduces the thermal inertia of the device. water in the pipe can be heated quickly.

  It can also be ensured that the thermally fusible part is a ring surrounding at least a portion of said fluid circulation duct and at least a portion of said electric heating circuit, said fuse piece being in abutment against a bearing zone of said pipe and / or said electric heating means to be heated there.

  A ring-shaped fuse piece promotes a symmetrical distribution of the forces of the switch on the fuse piece, this piece thus having a very good mechanical strength without having to use a large amount of material to achieve it.

  The ring shape also makes it possible to balance the heat exchanges between the fuse piece and the heating means.

  It is also possible for the thermally fusible piece to have a reduced section located at the location of the bearing zone.

  This characteristic makes it possible to create a privileged fusion zone that is easy to size and locate because of its shape. During the manufacture of the device is made so that the preferred melting zone is arranged to be substantially subjected to internal tensile forces generated by the switch (s). Thus during the fusion of this fuse zone breaks only under the constraints of pulls of switches, which allows a frank and rapid break. There is therefore less risk that the ring during its break prevents or blocks the movement (s) of the switches to their cutoff configurations.

  The likelihood of the device functioning is thus increased compared to what it would be if the rupture zone were located in a bending zone of the ring and compared to what it would be if no preferred rupture zone n was made.

  The fuse piece is made of plastic because the melting temperature of such a part is easily predictable and adjustable by the chemistry of the composites. On the other hand this ring is in a material chosen to be electrically nonconductive which avoids having to isolate the contactors with respect to the ring.

  It can also ensure that said contactor has a notch in which is placed a portion of the fuse piece thus allowing to mechanically assemble said fuse piece and the contactor, at least as long as the contactor is in the supply position.

  This embodiment makes it possible to have a mechanically stable switch / fuse assembly as long as this fuse piece is not melted.

  It can also be ensured that the device comprises two switches substantially identical to each other and electrically connected to said electric heating means to allow selective supply and that said thermally fusible piece is arranged to interact mechanically with each of the switches simultaneously, this piece fuse being further adapted to maintain these switches in their power supply configurations as long as said zone of said electric heating means does not exceed the critical temperature threshold and; to cause the passage of these switches from their power configuration to their cutoff configurations when said zone of said electric heating means exceeds the critical temperature threshold.

  The two switches that are held by one and the same fuse in their power configurations simultaneously go into cutoff configuration which multiplies the areas of power cuts on the same circuit and reduces the amount of circuit breakage energy to be cashed individually. by each switch of the circuit.

  Other features and advantages of the invention will emerge clearly from the description which is given below, by way of indication and in no way limitative, with reference to the appended drawings, in which: FIG. 1A represents a perspective view of the device of FIG. liquid heater of the invention with its contactors in cut-off configurations and without the thermally fusible piece; Figure 1B shows a sectional view of the heating device of the invention showing a switch in the cut position; FIG. 2A shows the device of the invention with its switches in power supply configurations and with the fusible piece not yet melted; Figure 2B shows a longitudinal sectional view of the device of Figure 2A; FIG. 3A represents the device of the invention with its switches in cut-off configurations and with the fuse part broken under the effect of overheating; Figure 3B shows a longitudinal sectional view of the device of Figure 3A; Figure 4 shows a front view of the ring-shaped fuse piece.

  As previously announced, the invention relates to a fluid heating device comprising a fluid circulation line and electric heating means which are here two electrical resistances placed in parallel and arranged to heat the fluid passing through the fluid line. The heating device of the invention is an improvement of the heating device presented in patent document FR 2 855 359.

  This device 1 comprises a main body 2 of cylindrical shape around which is fitted a complementary element 3 in the form of a tube. A space 5a is formed between the main body 2 and the inner face 10 of the complementary element 3 to define the fluid conduit 5 between the complementary element 3 and the main body 2.

  The fluid line 5 is spiral-shaped wound around the main body along the inner face 10 of the complementary element. For this, the main body is made of a material having a low thermal inertia (lower inertia than aluminum) and comprises at its periphery a groove in the form of a spiral facing the inner face 10. An inlet 19a and an outlet 19b fluid communicating with the pipe used to bind the device of the invention to an external fluid circuit.

  The electrical resistances 4 constituting the electric heating means 4 are screen-printed resistors on the outer face 12 of the complementary element 3 and form two resistive ribbons extending parallel to each other, covering at least 50% of the outer face 12. resistors 4 extend between two supply terminals 11a, 11b formed on the outer face 12 of the tube-shaped complementary element 3. These supply terminals 11a, 11b are formed at the ends of the resistors and are substantially identical between they have a near symmetry along a longitudinal sectional plane of the complementary element. The supply terminals 11a and 11b are both electrically accessible from the outside of the device to enable each contactor 13a, 13b mobile to establish a selective electrical contact against the corresponding connection terminal (terminal 11a with the contactor 13a, and terminal llb with contactor 13b).

  The contactors are elongate metal parts having three portions of length each exerting a proper function.

  The first portion of a contactor is a rigid end portion nested in a groove dedicated to the engagement of this contactor on a peripheral protrusion of the main body 2. For this, the main body is at least at this location electrically insulating, this body can be for this purpose integrally composed of plastic material.

  Each first contactor portion is adapted to be nested with a connector power socket.

  The second portion of a contactor is a locally elastic portion 9 also called elastic portion of the switch. This second portion has the function of forcing a third portion of the contactor to deviate from the connection terminal 11a or 11b corresponding to the contactor. This second portion has a flat cross section.

  The third portion of the contactor is a contactor portion rigid along its length to allow to transmit a compressive force of the contactor on the corresponding connection terminal 11a or 11b. This third portion has a substantially U-shaped cross section to give it this rigidity. This third portion comprises a notched zone 16 adapted to receive in bearing a portion of the fuse piece 7.

  A zone of the contactor preferably located in the second flexible portion is folded at V, in the direction of the length of the contactor, to form an electrical contact dedicated to the current flow between the contactor and the connection terminal of the complementary element, this contact zone being located at the tip of the V-fold. A thermally fusible piece 7 is shown alone in FIG. 4 in the form of a rigid ring of internal diameter greater than the external diameter of the complementary element.

  This fuse piece is also shown in Figures 2a and 2b but this time in combination with the rest of the device. In these figures 2a, 2b the fuse piece 7 surrounds the complementary element 3 and holds all the contactors in their respective supply positions.

  As shown in FIG. 4, the fuse piece comprises two portions of arcs 17a, 17b of a diameter substantially equal to the external diameter of the complementary element which is represented in dashed line referenced 2. Four arrows respectively represent the four forces generated. by the contactors on the fuse piece. These efforts tend to force the portions of arches 17a, 17b against the complementary piece. These portions of arcs 17a, 17b are opposed to each other so as to form a holding zone in localized support of the fuse piece on the complementary element. The fuse piece has a reduced section 15, at the location of the support zones 14 of the fuse piece against the complementary element. This section is intended to form the preferred breaking zone of the fuse piece when the complementary element is overheated. Thus, in normal operation, this ring makes it possible to maintain the contact pressure between the contactors and the electrical connection terminals of the resistor. During overheating, the ring melts at the reduced sections 15 thus releases the contact pressure and opens the electrical supply circuit of the heating means.

  In the embodiment of the invention shown in FIGS. 1a, 1b, 2a, 2b, 3a, 3b, four separate contactors are used to form four substantially identical switches with each other (each switch has a connector fixed on the main body and a connection terminal formed on the complementary element 3.

  Two of these switches are arranged to allow or cut the power supply to the terminals of the heating means and two others are used to allow or cut the power supply to the terminals of a positive temperature coefficient resistor which is fixed on the complementary element 3 to measure the temperature.

  In a simplified construction, only two blades can be used to manage the power supply of the resistors only.

  A preferred zone 8 is arranged so that the temperature in normal operation in this zone 8 is compatible with the operating temperature of the fuse to prevent it from melting prematurely.

  In this particular case, in order to limit the temperature of the resistive tracks, they are covered with a conductor 18 facilitating the flow of current and avoiding the heating of this zone 8.

  In another construction, the drawing of the resistive tracks can be made in such a manner as to move the resistive tracks away from or close enough to the fuse 7.

  In this particular case, the material chosen to make the fuse is a plastic material that achieves a good compromise between the temperature resistance and the cost. Preferably, a crystalline material whose melting temperature range is reduced is used.

  In this particular case the material of the fuse, whose melting point is about 285 ° C., is a polyphenylene sulfide (PPS) loaded with 32% glass fiber and 32% mineral.

  The reduced section 15 favoring the melting speed of the fuse material at this precise location is preferably 2.8mm × 1.4mm.

  These features, such as the shape of the fuse in zone 15 and the choice of the fuse material, depend on the design of the tracks, the need to facilitate the passage of the current in zone 14, the type of resistive tracks, the materials of the fuse. complementary element, the drawing of the main body and can therefore be considered as the only valid in this type of construction.

2891688 15

Claims (10)

  A fluid heating device (1) comprising a fluid circulation line (5), electric heating means (4) arranged to heat the fluid passing through the fluid line (5), and a switch (6). electrically connected to the electric heating means (4), this switch (6) being selectively movable between a power configuration to allow the power supply of said electric heating means and a cut-off configuration to prohibit the power supply of said electric means characterized in that a thermally fusible piece (7) is arranged close to said electric heating means to be heated by the latter in operation, said fuse piece (7) being adapted to melt at least partially when a zone (8) at least said electric heating means exceeds a critical temperature threshold and then to cause the passage of the interrup (6) from its power configuration to its cutoff configuration.   2) Device according to claim 1, characterized in that the switch (6) has a resilient portion (9) which naturally forces it to go into cut-off configuration, the thermally fusible piece (7) exerting a holding force of the switch in its power supply configuration as long as said zone (8) of said electric heating means (4) has not exceeded said critical temperature threshold.   3) Device according to any one of claims 1 or 2, characterized in that it comprises a main body (2) and a complementary element (3) covering a portion of the main body (2) to define said pipe (5) between the main body and an inner face (10) of the complementary element, said switch comprising a connection terminal (11) electrically connected to the electric heating means (4) and formed on an outer face (12) of the element complementary (3) which is opposite to said inner face (10).   4) Device according to claims 2 and 3,   characterized in that said switch comprises a metal contactor (13a) whose one end is fixed on said main body (2), this contactor (13a). selectively adopting a supply position where it is in contact with said connection terminal, the switch (6) then being in the power supply configuration and; selectively adopting a cut-off position in which it is separated from the connection terminal (11), the switch then being in the cut-out configuration, said elastic portion (9) of the switch being constituted by a locally elastic portion (9); ) of the contactor (13a) which naturally forces the latter to go into the cutoff position.   5) Device according to any one of claims 3 or 4, characterized in that the electric heating means comprise at least one heating resistor screen printed on the outer face (12) of the complementary element (3).   6) Device according to any one of the preceding claims, characterized in that the thermally fusible piece (7) is a ring surrounding at least a portion of said fluid circulation pipe (5) and at least a portion of said electrical circuit of heating, this fuse piece (7) being in abutment against a bearing zone (14) of said pipe (5) and / or said electric heating means (4) to be heated there.   7) Device according to claim 6, characterized in that the thermally fusible piece (7) has a reduced section (15) located at the location of the support zone (14).   8) Device according to any one of the preceding claims, characterized in that the fuse piece (7) is electrically nonconductive plastic material.   9) Device according to any one of the preceding claims combined with claim 4, characterized in that said contactor (13a) comprises a notch (16) in which is placed a portion of the thermally fusible piece (7) thus allowing mechanically assembling said fuse piece (7) and the contactor, at least as long as the contactor is in the supply position.   10) Device (1) according to any one of the preceding claims, characterized in that it comprises two substantially identical switches between them and electrically connected to said electric heating means (4) to allow selective feeding and that said thermally fusible piece (7) is arranged to mechanically interact with each of the switches simultaneously, this fuse piece (7) being further adapted to maintain these switches in their power supply configurations as long as said zone (8) of said electric heating means does not exceed the critical temperature threshold and to cause the passage of these switches from their power configuration to their cutoff configurations when said zone of said electric heating means exceeds the critical temperature threshold.